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Protein localization in dendritic spines is the focus of intense investigations within neuroscience. Applications of super-resolution microscopy to dissect nanoscale protein distributions, as shown in this work with dual-color STED, generate spatial correlation coefficients having quite small values. This means that colocalization analysis to some extent looses part of its correlative impact. In this study we thus introduced nearest neighbor analysis to quantify the spatial relations between two important proteins in neurons, the dopamine D1 receptor and Na+,K+-ATPase. The analysis gave new information on how dense the D1 receptor and Na+,K+-ATPase constituting nanoclusters are located both with respect to the homogenous (self to same) and the heterogeneous (same to other) topology. The STED dissected nanoscale topologies provide evidence for both a joint as well as a separated confinement of the D1 receptor and the Na+,K+-ATPase in the postsynaptic areas of dendritic spines. This confined topology may have implications for generation of local sodium gradients and for structural and functional interactions modulating slow synaptic transmission processes. Microsc. Res. Tech., 2011. © 2011 Wiley Periodicals, Inc [ABSTRACT FROM AUTHOR]

Background: The Na+,K+-ATPase plays an important role for ion homeostasis in virtually all mammalian cells, including neurons. Despite this, there is as yet little known about the isoform specific distribution in neurons. Results: With help of superresolving stimulated emission depletion microscopy the spatial distribution of Na+,K+- ATPase in dendritic spines of cultured striatum neurons have been dissected. The found compartmentalized distribution provides a strong evidence for the confinement of neuronal Na+,K+-ATPase (a3 isoform) in the postsynaptic region of the spine. Conclusions: A compartmentalized distribution may have implications for the generation of local sodium gradients within the spine and for the structural and functional interaction between the sodium pump and other synaptic proteins. Superresolution microscopy has thus opened up a new perspective to elucidate the nature of the physiological function, regulation and signaling role of Na+,K+-ATPase from its topological distribution in dendritic spines. [ABSTRACT FROM AUTHOR]

Sodium excretion is bidirectionally regulated by dopamine, acting on D1-like receptors (DIR) and angiotensin II, acting on AT1 receptors (AT1R). Since sodium excretion has to be regulated with great precision within a short frame of time, we tested the short-term effects of agonist binding on the function of the reciprocal receptor within the D1R-AT1R complex in renal proximal tubule cells. Exposure of rat renal proximal tubule cells to a D1 agonist was found to result in a rapid partial internalization of AT1R and complete abolishment of AT1R signaling. Similarly, exposure of rat proximal tubule cells and renal tissue to angiotensin II resulted in a rapid partial internalization of D1R and abolishment of D1R signaling. D1R and AT1R were, by use of coimmunoprecipitation studies and glutathione-S-transferase pull-down assays, shown to be partners in a multiprotein complex. Na+-K+-ATPase, the target for both receptors, was included in this complex, and a region in the COOH-terminal tail of DIR (residues 397-416) was found to interact with both AT1R and Na+-K+-ATPase. Results indicate that AT1R and D1R function as a unit of opposites, which should provide a highly versatile and sensitive system for short-term regulation of sodium excretion. [ABSTRACT FROM AUTHOR]

It is generally believed that cells that are unable to downregulate glucose transport are particularly vulnerable to hyperglycemia. Yet, little is known about the relation between expression of glucose transporters and acute toxic effects of high glucose exposure. In the present ex vivo study of rat renal cells, we compared the apoptotic response to a moderate increase in glucose concentration. We studied cell types that commonly are targeted in diabetic kidney disease (DKD): proximal tubule cells, which express Na + -dependent glucose transporter (SGLT)2, mesangial cells, which express SGLT1, and podocytes, which lack SGLT and take up glucose via insulin-dependent glucose transporter 4. Proximal tubule cells and mesangial cells responded within 4-8 h of exposure to 15 mM glucose with translocation of the apoptotic protein Bax to mitochondria and an increased apoptotic index. SGLT downregulation and exposure to SGLT inhibitors abolished the apoptotic response. The onset of overt DKD generally coincides with the onset of albuminuria. Albumin had an additive effect on the apoptotic response. Ouabain, which interferes with the apoptotic onset, rescued from the apoptotic response. Insulin-supplemented podocytes remained resistant to 15 and 30 mM glucose for at least 24 h. Our study points to a previously unappreciated role of SGLT-dependent glucose uptake as a risk factor for diabetic complications and highlights the importance of therapeutic approaches that specifically target the different cell types in DKD.

Background: Blockers of angiotensin II type 1 receptor (AT 1 R) and the voltage gated calcium channel 1.2 (Ca V 1.2) are commonly used for treatment of hypertension. Yet there is little information about the effect of physiological concentrations of angiotensin II (AngII) on AT 1 R signaling and whether there is a reciprocal regulation of AT 1 R signaling by Ca V 1.2., Methods: To elucidate these questions, we have studied the Ca 2+ signaling response to physiological and pharmacological AngII doses in HEK293a cells, vascular smooth muscle cells and cardiomyocytes using a Ca 2+ sensitive dye as the principal sensor. Intra-cellular calcium recordings were performed in presence and absence of Ca V 1.2 blockers. Semi-quantitative imaging methods were used to assess the plasma membrane expression of AT 1 R and G-protein activation., Results: Repeated exposure to pharmacological (100 nM) concentrations of AngII caused, as expected, a down-regulation of the Ca 2+ response. In contrast, repeated exposure to physiological (1 nM) AngII concentration resulted in an enhancement of the Ca 2+ response. The up-regulation of the Ca 2+ response to repeated 1 nM AngII doses and the down-regulation of the Ca 2+ response to repeated 100 nM Angll doses were not accompanied by a parallel change of the AT 1 R plasma membrane expression. The Ca 2+ response to 1 nM of AngII was amplified in the presence of therapeutic concentrations of the Ca V 1.2 blockers, nifedipine and verapamil, in vascular smooth muscle cells, cardiomyocytes and HEK293a cells. Amplification of the AT 1 R response was also observed following inhibition of the calcium permeable transient receptor potential cation channels, suggesting that the activity of AT 1 R is sensitive to calcium influx., Conclusions: Our findings have implications for the understanding of hyperactivity of the angiotensin system and for use of Ca 2+ channel blockers as mono-therapy in hypertension.

Protein localization in dendritic spines is the focus of intense investigations within neuroscience. Applications of super-resolution microscopy to dissect nanoscale protein distributions, as shown in this work with dual-color STED, generate spatial correlation coefficients having quite small values. This means that colocalization analysis to some extent looses part of its correlative impact. In this study we thus introduced nearest neighbor analysis to quantify the spatial relations between two important proteins in neurons, the dopamine D1 receptor and Na(+),K(+)-ATPase. The analysis gave new information on how dense the D1 receptor and Na(+),K(+)-ATPase constituting nanoclusters are located both with respect to the homogenous (self to same) and the heterogeneous (same to other) topology. The STED dissected nanoscale topologies provide evidence for both a joint as well as a separated confinement of the D1 receptor and the Na(+),K(+)-ATPase in the postsynaptic areas of dendritic spines. This confined topology may have implications for generation of local sodium gradients and for structural and functional interactions modulating slow synaptic transmission processes., (Copyright © 2011 Wiley Periodicals, Inc.)

The zeta subunit of the CD3 T-cell receptor complex and the major histocompatibility complex class 1 (MHC-I) are important not only for the immune response to antigens, they also function as signal molecules in the brain, where they play a role in the postnatal maturation process. The expression of these molecules can be regulated by cytokines. In situations associated with increased cytokine production, such as neonatal hypoxia, the hippocampus is particularly susceptible to permanent damage. This has prompted us to examine the MHC-I and CD3-zeta expression in hippocampus from early postnatal, weanling and adolescent rats and to record the effects of TNF-alpha and IL-1beta, cytokines commonly increased in neonatal hypoxia, on MHC-I and CD3-zeta expression in the hippocampus. We show that there is a robust postnatal up-regulation of CD3-zeta and MHC-I protein as well as of MHC-I mRNA and that TNF-alpha down-regulates the expression of CD3-zeta protein and MHC-I mRNA in early postnatal but not in weanling nor in adolescent rats. These results may offer a molecular explanation to the adverse effects of increased circulating levels of cytokines on brain in neonatal hypoxia.